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GAS SUPPLY SYSTEMS
Low pressure building gas supply systems are defined as those systems that cannot under any circumstances
exceed 14" W.C. (1/2 PSI Gauge). These systems do not require additional pressure regulation. Measurements
should be taken to insure that gas pressures are stable and fall within the requirements stated on the water
heater rating plate. Readings should be taken with all gas burning equipment off (static pressure) and with all
gas burning equipment running at maximum rate (dynamic pressure). The gas pressure supplied to this unit
must be below the maximum and above the minimum pressures listed on the unit's rating plate and must not
drop more than 1.5" W.C. when unit is operating at the high fire rate along with all additional gas appliances
operating on the same gas supply system. Pressure drops that exceed 1.5" W.C. may cause rough starting,
noisy combustion or nuisance outages. Increases or spikes in static pressure during off cycles may cause
failure to ignite or in severe cases damage to appliance Gas Control Valves. If your low pressure system does
NOT meet these requirements, do not operate this unit. The installer is responsible for ensuring that the gas
supply pressures meet the requirements described above and listed in the table. Failure of the gas supply to
meet these requirements is not covered under the warranty.
High Pressure building supply systems use pressures that exceed 14" W.C. (1/2 PSI Gauge). These
systems must use field supplied regulators to lower the gas pressure to less than 14" W.C. (1/2 PSI
Gauge). Water heaters require gas regulators that are properly sized for the water heater's BTU input
and capable of delivering the rating plate specified pressures. Gas supply systems where pressure
exceeds 5 PSI often require multiple regulators to achieve desired pressures. Systems in excess of 5 PSI
building pressure should be designed by gas delivery professionals for best performance. Water heaters
connected to gas supply systems that exceed 14" W.C. (1/2 PSI Gauge) must be equipped with a gas
supply regulator capable of preventing the gas supplied to the unit from exceeding 14" W.C. under any
upstream supply pressure or condition.
Natural Gas SUF 60120-100250 models require a minimum gas supply pressure of 3.5" W.C.,
SUF 119300-119500 natural gas models require 4.8" W.C., and all models require 8.5" W.C. for
propane gas. The minimum supply pressure is measured while gas is flowing (dynamic pressure)
along with all additional gas appliances operating on the same gas supply system. The supply
pressure should be measured with all gas fired appliances connected to the common main firing at
full capacity. If the supply pressure drops more than 1.5" W.C. (0.05 PSI Gauge) when the water
heater is operating at high fire rate, then the supply gas system including the gas line and/or the
gas regulator may be restricted or undersized. See Supply Gas Regulator section below. The
Gas Control Valve on all models has a maximum gas supply pressure limit of 14" W.C. (1/2 PSI
Gauge). The maximum supply pressure is measured while gas is not flowing (static pressure) to
any appliances connected to the same gas supply system.
SUPPLY GAS REGULATOR
The maximum allowable gas supply pressure for the water heaters covered in this Service Handbook is
14.0 inches W.C. (3.49 kPa) for natural and propane gas. Install a positive lock-up gas pressure regulator in
the gas supply line if inlet gas pressure can exceed these pressures at any time. Regulators must be sized
to equal or exceed the BTU input requirements of the heater model and installed, used, and maintained
according to manufacturer's specifications.
If a positive lock-up regulator is installed follow these instructions:
1. Positive lock-up gas pressure regulators must be rated at or above the input Btu/hr rating of all the
gas appliances that are on the same system as the water heater.
2. Supply gas regulators shall have inlet and outlet connections not less than the minimum supply gas
line size for the water heater they supply.
3. Refer to the gas pressure regulator's manufacturers installation instructions to determine its installation
location requirements.
4. After installing the positive lock-up gas pressure regulator(s) an initial nominal supply pressure
setting of 7.0" W.C. (1.74 kPA) for Natural Gas and 11.0" W.C. (2.74 kPA) for Propane (LP) while the
water heater is operating is recommended and will generally provide good water heater operation.
Adjustments to the regulator maybe required to maintain a steady gas supply pressure.
Servicing should only be performed by a Qualified Service Technician
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